Some boats are propelled by outboard motors. These motors typically have an internal combustion engine connected to a propeller. One important part of the outboard motor is the cooling system. Within the cooling system, a pump draws in water from beneath the motor and that water is circulated around the engine to draw off heat. The water is then expelled from the motor back into the body of water from which it was drawn. If the cooling system fails, the motor can overheat and fail, leaving boaters stranded out at sea, with possibly dire consequences.
To help boaters monitor the cooling system, many outboard motors provide a “telltale”. The telltale is a stream of water that is visibly expelled from the motor under pressure of the water pump while the motor and the cooling system are functioning properly. Seeing the telltale assures a boater that the cooling system is protecting the motor from overheating and failing. Unfortunately, the telltale is difficult to see if conditions are not optimal. Not only is the telltale not visible at night, even during the day it can be hard to see if background conditions and lighting are unfavorable, for example, during heavy fog or a storm or at dusk.